Continuously variable transmissions (CVTs) used in recreational or off road utility vehicles use rubber belts to transmit torque between a drive clutch, or primary clutch, and a driven clutch, or secondary clutch. CVT belts are typically V-belts that are expected to remain in contact with the V-belt pulleys of the drive and driven clutches. Some CVTs have “loose” V-belts that are not pre-tensioned between the two clutches while in a static state. Under certain conditions, “loose” V-belts may lose contact with the driven clutch. More specifically, when a CVT belt is used under high load conditions at the CVT's lowest drive ratio, including initial starts or hill climbing, for example, the drive clutch may clamp onto the belt and tension only one side of the belt between the drive and driven clutches. With high tension on only one side of the CVT belt, the belt may slip on the driven clutch. When the slipping stops and the CVT belt engages the drive clutch, a ripple or wave may appear in the un-tensioned side of the belt. Slack in the un-tensioned side of the belt may increase or amplify the ripple or wave so much that the belt may lose contact momentarily with the driven clutch. Even brief loss of engagement or contact of the belt with the driven clutch allows the transmission and driveline to release stored torsional stress and rotate opposite of the drive clutch. This may result in torque spikes when the primary clutch re-engages the belt, and the torque spikes transfer through the transmission and cause undesirable vehicle performance at the lowest drive ratio, such as shuddering or jerking. There is a need for a CVT with a “loose” belt that maintains contact with a driven clutch at low drive ratios and improves vehicle performance during initial starts, hill climbs, and other high load conditions.
In the past, cooling fans have been proposed to keep CVT belts cool in order to improve their durability. However, CVT cooling fans produce substantial noise that may be undesirable or unsatisfactory to drivers of off-road utility vehicles. There is a need for CVT cooling fan that reduces or minimizes air noise and provides better cooling of the drive clutch, driven clutch and belt of the continuously variable transmission.